The present invention relates to the supercharging of internal combustion engines. The power of an internal combustion engine may be increased by increasing the volume of the air/fuel mixture that is delivered to the cylinders. This process of supercharging is achieved by increasing the pressure of the air of air/fuel mixture that is delivered to the cylinders, above atmospheric pressure. In the past supercharging of internal combustion engines has been achieved by one of two methods, that is by the use of a mechanically driven positive displacement pump or supercharger, or by an exhaust driven pump or turubocharger. In both cases, all the air supplied to the engine passes through the supercharging pump.
Mechanically driven superchargers work well at low engine speeds, but their size and power requirements have made these units unpopular and they have been superceded in recent years by turbochargers. Turbochargers, being driven by the exhaust gasses of the engine, impose a relatively low power loss and are relatively compact. The main drawbacks of turbochargers are their poor throttle response, their need to work at relatively high engine speeds for good performance, and problems with increase in temperature of the induced air due to conduction from the exhaust gasses. Furthermore, the known superchargers or turbochargers provide a continuous supply of pressurised air which is delivered to the engine when the inlet ports are closed as well as on the induction strokes. Moreover, pressurised air will be supplied to the engine throughout the induction stroke. However, it is more efficient to supercharge only towards the end of the induction stroke, when the amount of air drawn into the cylinder under normal aspiration is reducing.